Long term evolution (hereinafter, abbreviated as LTE) communication system is an evolution of the third generation mobile communication system (hereinafter, abbreviated as 3G). Different from a circuit switching mode adopted in conventional cellular systems, LTE communication system only supports packet switching service and can provide a higher service transmission rate, i.e. providing respectively an uplink peak data rate of 100 Mbit/s and a downlink peak data rate of 50 Mbit/s within a bandwidth of 20 MHz, thereby providing more colourful services for users.
LTE communication system can concurrently employ a frequency division duplex (hereinafter, abbreviated as FDD) mode and a time division duplex (hereinafter, abbreviated as TDD) mode in a unified framework. LTE communication system that employs a TDD mode is also referred to as TD-LTE system. FIG. 1 is a schematic view of a frame structure in a TD-LTE system under a switching cycle of 5 ms. As shown in FIG. 1, each wireless frame has a length of 10 ms (Tf=307,200×Ts=10 ms), consisting of two half-frames each having a length of 5 ms (153,600×Ts=5 ms). Each half-frame consists of five sub-frames each having a length of 1 ms (30,720×Ts=1 ms), wherein, each sub-frame contains two slots. FIG. 2 is a schematic view of a wireless resource structure of each slot in a downlink wireless frame. As shown in FIG. 2, each downlink slot Tslot comprises NsymbDL orthogonal frequency division multiplexing (hereinafter, abbreviated as OFDM) symbols and each OFDM symbol contains NRBDL*NSCRB sub-carriers in a frequency domain. One sub-carrier in one OFDM symbol is taken as a minimum wireless resource unit, which is referred to as resource element (hereinafter, abbreviated as RE). Thus, each downlink slot Tslot comprises NRBDL*NSCRB sub-carriers, i.e. comprising NRBDL*NSCRE REs wherein, 12*NsymbDL REs together constitute one resource block (hereinafter, abbreviated as RB).
In the TD-LTE system, due to wireless channel distortion, relative to a transmitting terminal, complex band-based signals (hereinafter, abbreviated as complex signal) carried by each RE at a receiving terminal are all superimposed with variations of amplitude and phase. Thus, the receiving terminal can obtain these variations so as to restore an original signal transmitted from the transmitting terminal.
FIG. 3 is an example of diagram of a reference channel of two consecutive RBs. As shown in FIG. 3, REs in diagonal filling parts represent channels of pilots, which are also referred to as pilot channels. Transmitted signals transmitted from the transmitting terminal on pilot channels are known. As a result, by comparing transmitted signals transmitted from the transmitting terminal on a pilot channel with a complex signal received by the receiving terminal on the same pilot channel, properties of a wireless channel through which the transmitted signals have passed can be obtained, wherein, the complex signal received by the receiving terminal comprises I-orthogonal signal and Q-orthogonal signal.
Currently, a channel estimation method as follows has been particularly adopted for performing channel estimation processing on wireless channels corresponding to the REs in an OFDM symbols.
For an OFDM symbol containing pilots, channel estimation is performed on the pilots contained therein, thereby obtaining channel estimation values of these pilots, and channel estimation values of all the non-pilots within the OFDM symbol containing pilots are obtained by smoothing in a frequency domain, assuming that the channel estimation value of the ith RE in the Kth OFDM symbol is represented as CKi.
Taking two adjacent OFDM symbols containing pilots as a LTE reference signal (hereinafter, abbreviated as RS) symbol, it is assumed that the sequence numbers of the two OFDM symbols that serve as the LTE RS symbol are N1 and N2 respectively. A channel estimation value of a corresponding RE in an OFDM symbol containing no pilots between the two OFDM symbols whose sequence numbers are N1 and N2 respectively is obtained by using a linear interpolation method.
In the prior art, the following method has been particularly adopted to obtain estimated values for transmitted signals of a transmitting terminal on each RE within respective OFDM symbols.
After a receiving terminal has received OFDM symbols, a Fast Fourier Transform (hereinafter, abbreviated as FFT) is performed respectively on each of the received OFDM symbols, thereby obtaining FFT values and storing these FFT values in an FFT buffer unit. A channel estimation (hereinafter, abbreviated as CHE) unit extracts OFDM symbols containing pilots from the FFT buffer unit, and based on the currently channel estimation method described above, channel estimation processing is performed on wireless channels corresponding to REs within OFDM symbols, thereby obtaining channel the estimation value of each RE in the respective OFDM symbol and storing these values in a CHE buffer unit. A multiple input multiple output (hereinafter, abbreviated as MIMO) demodulation unit extracts FFT values and channel estimation values corresponding to the same RE respectively from the FFT buffer unit and the CHE buffer unit one OFDM symbol by one OFDM symbol and one RE by one RE, and computation processing is performed based on a preset MIMO demodulation algorithm, thereby obtaining estimated values for transmitted signals of the transmitting terminal on each RE within the respective OFDM symbols.
It has presently been found that the method for acquiring an estimated value of a transmitted signal according to the prior art has at least the following problems.
It needs a CHE unit to store channel estimation values of all the OFDM symbols between two LTE RS symbols, such that MIMO demodulation unit can calculate estimated values for transmitted signals of the transmitting terminal on each RE in all the OFDM symbols between two LTE RS symbols based on channel estimation values and FFT values. It thus takes up more system-on-chip (hereinafter, abbreviated as SOC) memory of the receiving terminal, and results in increasing the cost and degrading information processing performance of a SOC.